"I do reassure the families of our hope and expectation that the ongoing search will succeed," he told Parliament in Canberra.

"I can't promise that the search will go on at this intensity forever but we will continue our very best efforts to resolve this mystery and provide some answers."

Martin Dolan, chief commissioner of the Australian Transport Safety Bureau (ATSB), who was previously optimistic about discovering the plane, said he could not "guarantee it will happen".

The disappearance of MH370 has been dubbed one of the greatest aviation mysteries of all time.

Final contact with air traffic control was at 1.19am on 8 MarchMalaysian government, UK Air Accidents Investigation Branch, Australian Maritime Safety Authority

Satellite data has led experts to believe the plane crashed into the Southern Indian Ocean after it vanished from radar and veered off its flight path to Beijing from Kuala Lumpur - for reasons still unknown. No distress signal was sent out.

Officials said it flew back into Malaysian airspace and continued for seven hours before running out of fuel and crashed into the Indian Ocean. Malaysia's military has since been heavily criticised for failing to scramble jets towards the plane when it was detected flying back into Malaysian airspace. It said it failed to act because the plane was not deemed hostile.

But Malaysia Prime Minister Najib Razak said the flight's transponder had been "deliberately disabled" before the plane changed course. He said at the time the "movements were consistent with the deliberate action of someone on the plane" - although he stopped short of labelling it a hijacking.

After radar was lost data was picked up between the plane and a ground station satellite above the Indian Ocean, (identified by British company Inmarsat), which converted seven so-called "pings" enabling the firm to calculate possible routes the plane had flown in: the northern corridor between Thailand and Kazakhstan and the southern corridor between Indonesia and the Southern Indian Ocean.

There were 227 passengers on board, 153 Chinese, 38 Malaysians - 12 of which were crew members led by captain Zaharie Ahmad Shah, 53, and co-pilot Fariq Abdul Hamid, 27. Other passengers were from Iran, US, Canada, Indonesia, Australia, India, France, New Zealand, Ukraine, Russia, Taiwan and the Netherlands.

The Malaysian government officially declared the disappearance of Malaysia Airlines flight an accident in January - presuming all 239 people on board were dead, which greatly distressed the victims' families.

"The most frustrating thing is that they [were planning] an announcement to the world first, then only to the next of kin," said Wesley Walter, whose brother-in-law was on the flight. "Why are the next of kin being treated this way?".